Image inspection apparatus, image inspection system and image inspection method

ABSTRACT

An image inspection apparatus for inspecting a scanned image of an output image includes an inspection reference image generator to generate an inspection reference image; an image inspection unit to determine a defect by comparing a difference between the inspection reference image and the scanned image with a threshold; a threshold determiner to determine the threshold; and a defect range determiner to determine a range of defect level of a plurality of artificial defects. Based on a difference computed for a defect selected from the plurality of artificial defects, the threshold determiner determines a threshold to be compared with the difference of the selected defect. The defect range determiner conducts a defect determination for the scanned image at the upper and lower limits for a threshold to determine a range of defect level of the plurality of artificial defects.

This application claims priority pursuant to 35 U.S.C. §119 to JapanesePatent Applications Nos. 2012-203590, filed on Sep. 14, 2012 and2013-165590, filed on Aug. 8, 2013 in the Japan Patent Office, thedisclosure of which is incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present invention relates to an image inspection system and an imageinspection method, and more particularly to setting of inspectionthresholds used for determining defects in image.

2. Background Art

Conventional inspections of printed matter such as printed papers areconducted by visual inspection, but inspection apparatuses have beenintroduced to conduct the inspections as a post-processing operation ofthe offset printing. As for the inspection apparatus, the printedmatters are visually inspected by an operator to select a printed matterhaving satisfactory image quality, and then the selected printed matteris scanned to generate a master image to be used as a reference image.The master image and inspection target printed matter are compared witheach other by scanning the inspection target printed matter, and basedon difference between the master image and the inspection target, defectof the inspection target printed matter can be determined.

However, the printing apparatuses of digital to press such as imageforming apparatuses using electrophotography typically print images witha small volume, and also print different images for each page (i.e.variable printing), in which generating a master image from printedmatter as a reference image is not efficient. In this type of imageforming apparatuses, the master image can be generated from print datato efficiently conduct the inspection for the variable printing.

In this image inspection process, the defect of printed matter can bedetermined based on the above mentioned difference level. Specifically,scanned images prepared by scanning sheets printed with images and themaster image generated from the print data are compared, in whichpositions and sizes of comparing images are matched and then thecomparing images are compared for each pixel based on a given threshold.

JP-2008-003876-A discloses an image inspection process for an inkjetprinter, which can verify inspection precision for the image inspection.Specifically, defects that may likely occur for the inkjet printer areartificially printed on sheets, the sheets having printed with theartificial defects are inspected, and then it is verified whether theinspection can be conducted effectively.

The above mentioned threshold used for comparing the images affect theinspection precision, therefore effective thresholds need to be set forhigh precision inspection. JP-2008-003876-A discloses a configuration todetermine whether the inspection is conducted effectively usingthresholds such as thresholds set in advance, in which suitablethresholds are not set automatically.

A plurality of defects having different levels can be reproduced asartificial defects to conduct an image inspection, and an image to bedetermined as defect can be selected by a user, and a threshold can beset based on a determination result of the defect image selected by theuser. However, because image scanning capability of each apparatus isdifferent, when generating the plurality of defects having differentlevels, the defect matched to the image scanning capability of apparatusis required to be generated and output. If the defect matched to theimage scanning capability cannot be determined, preferable settingcannot be conducted.

SUMMARY

In one aspect of the present invention, an image inspection apparatusfor inspecting an image output on a recording medium by scanning theoutput image as a scanned image is devised. The image inspectionapparatus includes an inspection reference image generator to obtaindata of an output-target image used by the image forming apparatus foran image forming operation, and to generate an inspection referenceimage using the data of the output-target image, the inspectionreference image to be used for an image inspection of the scanned image;an image inspection unit to determine whether the scanned image includesa defect based on a comparison result obtained by comparing a differencebetween the inspection reference image and the scanned image with agiven threshold; a threshold determiner to determine the given thresholdbased on a comparison result between the inspection reference imagehaving a normal image condition and the scanned image of thresholdsetting image prepared by adding a plurality of artificial defectshaving different defect levels to the inspection reference image; and adefect range determiner to determine a range of defect level of aplurality of artificial defects having the different levels for thethreshold setting image. The threshold determiner controls generation ofthe inspection reference image having the normal image condition to beused for determining the given threshold. The threshold determinercomputes a difference between the inspection reference image and thescanned image of the threshold setting image for each of the pluralityof artificial defects having the different defect levels. Based on adifference computed for a defect selected from the plurality ofartificial defects having different defect levels, the thresholddeterminer determines a threshold to be compared with the difference ofthe selected defect to determine whether the scanned image includes adefect. The defect range determiner conducts a defect determinationprocess for a range determination scanned image, obtained by scanning arange determination image displaying a plurality of defects havingchanged levels with a given interval at each of the upper limit and thelower limit settable for a threshold. The defect range determinerdetermines a range of defect level of the plurality of artificialdefects having the different defect levels for the threshold settingimage based on a defect level of a defect determined as defect in thedefect determination process for the range determination image at eachof the upper limit and the lower limit settable for the threshold.

In another aspect of the present invention, an image inspection systemfor inspecting an image output on a recording medium is devised. Theimage inspection system includes an image forming unit to conduct animage forming operation of a threshold setting image on the recordingmedium, the threshold setting image prepare-able by adding an artificialdefect to an output-target image input to the image forming unit; animage scanner to scan the threshold setting image output on therecording medium to generate a scanned image; an inspection referenceimage generator to obtain data of the output-target image used by theimage forming apparatus for an image forming operation, and to generatean inspection reference image using the data of the output-target image,the inspection reference image to be used for an image inspection of thescanned image; an image inspection unit to determine whether the scannedimage includes a defect based on a comparison result obtained bycomparing a difference between the inspection reference image and thescanned image with a given threshold; a threshold determiner todetermine the given threshold based on a comparison result between theinspection reference image having a normal image condition and thescanned image of threshold setting image prepared by adding a pluralityof artificial defects having different defect levels to the inspectionreference image; and a defect range determiner to determine a range ofdefect level of a plurality of artificial defects having the differentlevels for the threshold setting image. The image forming section unitconducts an image forming operation of the threshold setting image basedon the determined range of defect level of the artificial defect. Thethreshold determiner controls generation of the inspection referenceimage having the normal image condition to be used for determining thegiven threshold. The threshold determiner computes a difference betweenthe inspection reference image and the scanned image of the thresholdsetting image for each of the plurality of artificial defects having thedifferent defect levels. Based on a difference computed for a defectselected from the plurality of artificial defects having differentdefect levels, the threshold determiner determines a threshold to becompared with the difference of the selected defect to determine whetherthe scanned image includes a defect. The defect range determinerconducts a defect determination process for a range determinationscanned image, obtained by scanning a range determination imagedisplaying a plurality of defects having changed levels with a giveninterval at each of the upper limit and the lower limit settable for athreshold. The defect range determiner determines a range of defectlevel of the plurality of artificial defects having the different defectlevels for the threshold setting image based on a defect level of adefect determined as defect in the defect determination process for therange determination image at each of the upper limit and the lower limitsettable for the threshold.

In another aspect of the present invention, a method of inspecting animage, output on a recording medium, using an image inspection apparatusis devised. The method includes the steps of: obtaining an output-targetimage input to an image forming apparatus; generating an inspectionreference image using data of the output-target image; forming athreshold setting image on the recording medium using the image formingapparatus, the threshold setting image prepare-able by adding anartificial defect to the inspection reference image; scanning thethreshold setting image formed on the recording medium to obtain ascanned image of the threshold setting image; computing a differencebetween the scanned image and the inspection reference image bycomparing the scanned image and the inspection reference image;determining a threshold, based on a difference computed for a defectselected from the plurality of artificial defects having differentdefect levels, the determined threshold to be compared with thedifference for the selected defect to determine whether the scannedimage includes a defect; conducting a defect determination process for arange determination scanned image obtained by scanning a rangedetermination image, displaying a plurality of defects by changinglevels of different types of defect with a given interval, at each ofthe upper limit and the lower limit settable for a threshold; anddetermining a range of defect level of the plurality of artificialdefects having the different defect levels for the threshold settingimage based on levels of defect determined as defect in the defectdetermination process for the range determination image at each of theupper limit and the lower limit settable for the threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages and features thereof can be readily obtained and understoodfrom the following detailed description with reference to theaccompanying drawings, wherein:

FIG. 1 shows a schematic configuration of an image forming systemincluding an inspection apparatus according to an example embodiment;

FIG. 2 shows an example block diagram of a hardware configuration of theinspection apparatus according to an example embodiment;

FIG. 3 shows an example block diagram of an engine controller, a printengine and an inspection apparatus according to an example embodiment;

FIG. 4 shows a schematic mechanical configuration of a print processingunit according to an example embodiment;

FIG. 5 shows an example block diagram of master image processing unitaccording to an example embodiment;

FIG. 6 is a flowchart of process of a threshold determination processaccording to an example embodiment;

FIGS. 7A, 7B and 7C show examples of output images used for thresholddetermination process according to an example embodiment;

FIG. 8 shows an example of setting of artificial defects according to anexample embodiment;

FIG. 9 shows an example of a computation result of discrete thresholdcomputed for a plurality of artificial defects according to an exampleembodiment;

FIG. 10 is a flowchart of process of computing discrete thresholdaccording to an example embodiment;

FIG. 11 show an example of information indicating mark position on anoutput image for a threshold determination process according to anexample embodiment;

FIGS. 12A and 12B show examples of threshold selection screens accordingto an example embodiment;

FIG. 13 shows an example of calibration-use image according to anexample embodiment;

FIG. 14 shows an example of calibration-use information according to anexample embodiment;

FIG. 15 is a flowchart of steps of a calibration process according to anexample embodiment;

FIGS. 16A and 16B show examples of defect determination according to anexample embodiment;

FIG. 17 shows examples of images output for threshold determinationprocess according to another example embodiment;

FIG. 18 shows another example of threshold selection screen according toan example embodiment;

FIGS. 19A and 19B show schematic configurations of systems according toanother example embodiment;

FIG. 20 shows a schematic configuration of a system according to anotherexample embodiment;

FIG. 21 shows an example image displaying a measurement pattern forcalibration processing of an optical sensor and calibration-use imageaccording to another example embodiment;

FIG. 22 shows a schematic process of comparing images for inspectionaccording to an example embodiment;

FIG. 23 shows an example of threshold setting according to an exampleembodiment; and

FIG. 24 shows an example of upper and lower limits setting according toan example embodiment.

The accompanying drawings are intended to depict exemplary embodimentsof the present invention and should not be interpreted to limit thescope thereof. The accompanying drawings are not to be considered asdrawn to scale unless explicitly noted, and identical or similarreference numerals designate identical or similar components throughoutthe several views.

DETAILED DESCRIPTION

A description is now given of exemplary embodiments of the presentinvention. It should be noted that although such terms as first, second,etc. may be used herein to describe various elements, components,regions, layers and/or sections, it should be understood that suchelements, components, regions, layers and/or sections are not limitedtherefore because such terms are relative, that is, used only todistinguish one element, component, region, layer or section fromanother region, layer or section. Thus, for example, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

In addition, it should be noted that the terminology used herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the present invention. Thus, for example, asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Moreover, the terms “includes” and/or “including”, when usedin this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Furthermore, although in describing views shown in the drawings,specific terminology is employed for the sake of clarity, the presentdisclosure is not limited to the specific terminology so selected and itis to be understood that each specific element includes all technicalequivalents that have a similar function, operate in a similar manner,and achieve a similar result. Referring now to the drawings, apparatusesor systems according to example embodiments are described hereinafterwith reference to FIGS. 1 to 24.

In this disclosure, an image forming system includes an inspectionapparatus, in which a master image and an scanned image obtained byscanning an image output by an image forming operation are compared toinspect an output (e.g., printed image) of the image forming operation,and based on the a comparison result, thresholds used to determinedefect in an image, matched to inspection precision desired by a user,can be settable easily and preferably.

FIG. 1 shows an example configuration of an image forming systemaccording to an example embodiment. As shown in FIG. 1, the imageforming system includes, for example, a digital front end (DFE) 1, anengine controller 2, a print engine 3 and an inspection apparatus 4.Based on a received print job, the DFE 1 generates bitmap data, which isimage data to be output (i.e., output-target image), and outputs thegenerated bitmap data to the engine controller 2.

Based on the bitmap data received from the DFE 1, the engine controller2 controls the print engine 3 to conduct an image forming operation.Further, the engine controller 2 transmits the bitmap data received fromthe DFE 1 to the inspection apparatus 4, wherein the bitmap data is usedas data of original information for preparing an inspection referenceimage to be used for inspection at the inspection apparatus 4 when theinspection apparatus 4 inspects an output result of an image formingoperation of the print engine 3.

Under the control of the engine controller 2, the print engine 3conducts an image forming operation on a recording medium such as paperusing the bitmap data, and scans an output paper such as a paper printedwith an image using a scanner, and inputs the scanned image data to theinspection apparatus 4. The recording medium may be, for example, asheet such as paper, film, plastic sheet, and any material that can beused for outputting (i.e., forming) an image by an image formingoperation. Based on the bitmap data input from the engine controller 2,the inspection apparatus 4 generates a master image. Then, theinspection apparatus 4 compares the scanned image data, input from theprint engine 3, and the generated master image to conduct an imageinspection of output image, in which the inspection apparatus 4 is usedas an image inspection apparatus.

A description is given of a hardware configuration of the enginecontroller 2, the print engine 3 and the inspection apparatus 4according to an example embodiment with reference to FIG. 2. Further, asfor the inspection apparatus 4, engines for scanner and printer may beadded to the hardware configuration shown in FIG. 2. FIG. 2 shows ablock diagram of an example hardware configuration of the inspectionapparatus 4. The engine controller 2 and the print engine 3 may have ahardware configuration similar to the inspection apparatus 4 shown inFIG. 2.

As shown in FIG. 2, the inspection apparatus 4 can be configuredsimilarly to information processing apparatuses such as general servers,and personal computers (PC), or the like. Specifically, the inspectionapparatus 4 includes a central processing unit (CPU) 10, a random accessmemory (RAM) 20, a read only memory (ROM) 30, a hard disk drive (HDD)40, and an interface (I/F) 50, connectable to each other via a bus 90.Further, the I/F 50 is connectable to a liquid crystal display (LCD) 60,an operation unit 70, and a specific device 80.

The CPU 10 is a computing processor or unit which controls theinspection apparatus 4 as a whole. The CPU 10 can be configured withvarious types of processors, circuits, or the like, such as a programmedprocessor, a circuit, and an application specific integrated circuit(ASIC), used singly or in combination. The RAM 20 is a volatile memory,to which data or information can be written and read at high speed, andis used as a working memory when the CPU 10 processes data orinformation. The ROM 30 is a non-volatile memory used as a read onlymemory, and stores programs such as firmware or the like. The HDD 40 isa non-volatile storage device, to and from which data or information canbe written and read, and stores operating system (OS), management orcontrol software programs, application software programs, various data,or the like.

The I/F 50 can be used to connect various types of hardware and networkto the bus 90, and controls such connection. The LCD 60 is a userinterface to display information, with which the status of theinspection apparatus 4 can be checked by a user. The operation unit 70is a user interface such as a keyboard, a mouse, etc., with whichinformation can be input to the inspection apparatus 4 by the user.

The specific device 80 may be disposed as hardware to conduct a specificcapability or function for each of the engine controller 2, the printengine 3 and the inspection apparatus 4. For example, as for the printengine 3, the specific device 80 may be a plotter to conduct an imageforming operation on sheets, and a scanner to scan images output on thesheets. Further, as for the engine controller 2 and the inspectionapparatus 4, the specific device 80 may be a specific computing circuitto conduct high speed image processing, and the specific device 80 maybe, for example, an application specific integrated circuit (ASIC).

In the above hardware configuration, software programs stored in astorage area such as the ROM 30, the HDD 40, or an optical disk can beread and loaded to the RAM 20, and the CPU 10 runs such programs tocontrol various units, with which a software-executing controller can beconfigured. With a combination of such software-executing controller andhardware, a functional block to operate the engine controller 2, theprint engine 3 and the inspection apparatus 4 can be configured. In anexample embodiment, at least one of the units is implemented as hardwareor as a combination of hardware/software.

FIG. 3 shows an example block diagram of the engine controller 2, theprint engine 3 and the inspection apparatus 4. As shown in FIG. 3, theengine controller 2 includes, for example, a data obtainer 201, anengine control unit 202 and a bitmap transmitter 203. Further, the printengine 3 includes, for example, a print processing unit 301 and ascanner 302. Further, the inspection apparatus 4 includes, for example,a scanned image obtainer 401, a master image processing unit 402, aninspection control unit 403 and an inspection unit 404. The inspectionunit 404 can be used as an image inspection unit that compares imagesfor inspection.

Upon obtaining the bitmap data from the DFE 1 by the data obtainer 201,the engine control unit 202 and the bitmap transmitter 203 are operated.The bitmap data is information of pixels composing an image to be outputby an image forming operation, and the data obtainer 201 can function asa pixel information obtainer. Based on the bitmap data transferred fromthe data obtainer 201, the engine control unit 202 instructs the printengine 3 to conduct an image forming operation, in which the enginecontrol unit 202 can function as an output execution control unit. Thebitmap transmitter 203 transmits the bitmap data, obtained by the dataobtainer 201, to the inspection apparatus 4.

The print processing unit 301 obtains the bitmap data input from theengine controller 2, conducts an image forming operation to a sheet, andoutputs a printed sheet. Therefore, the print processing unit 301 canfunction as an image forming apparatus. The print processing unit 301can use any types of image forming mechanisms, for example, theelectrophotography, the inkjet method, or the like. The scanner 302scans an image formed on the sheet by conducting a printing operation bythe print processing unit 301, and outputs scanned data to theinspection apparatus 4. The scanner 302 is, for example, a line scannerdisposed along a transport route of sheet output by the print processingunit 301, in which the scanner 302 scans the transported sheet face toread an image formed on the sheet.

A description is given of mechanical configurations of the printprocessing unit 301 and the scanner 302 with reference to FIG. 4. Asshown in FIG. 4, the print processing unit 301 includes, for example,image forming units 106BK, 106M, 106C, 106Y and a transport belt 105 ofan endless movement unit, in which the image forming units 106BK, 106M,106C, 106Y are disposed along the transport belt 105, which is referredto as the tandem type. Specifically, the image forming units 106BK,106M, 106C, 106Y (electrophotography processing units) are disposedalong the transport belt 105 from the upstream side of a transportdirection of the transport belt 105. An intermediate transfer image isformed on the transport belt 105, and transferred to a recording mediumsuch as a sheet 104, which is separated and fed from a sheet tray 101using a sheet feed roller 102 and a separation roller 103.

The internal configuration is common for the image forming units 106BK,106M, 106C, 106Y except color of toner image, which means the imageforming unit 106BK forms black image, the image forming unit 106M formsmagenta image, the image forming unit 106C forms cyan image, and theimage forming unit 106Y forms yellow image. Hereinafter, the imageforming unit 106BK is described as the representative of the imageforming units 106BK 106M, 106C, 106Y. Each members composing the imageforming units 106BK 106M, 106C, 106Y may be attached with BK, M, C, Y asrequired.

The transport belt 105 is an endless belt extended by a drive roller 107and a driven roller 108. The drive roller 107 can be rotated by a drivemotor. The drive motor, the drive roller 107 and the driven roller 108can be collectively function as a drive unit for the transport belt 105which is the endless movement unit.

When forming images, the image forming unit 106BK transfers black tonerimage to the rotating transport belt 105. The image forming unit 106BKincludes, for example, a photoconductor drum 109BK used as aphotoconductor, a charger 110BK disposed near the photoconductor drum109BK, a development unit 112BK, a photoconductor cleaner, and adecharger 113BK. Further, an optical writing unit 111 irradiates lightfor each of the photoconductor drums 109BK, 109M, 109C, 109Y(hereinafter, photoconductor drum 109).

When forming images, an outer face of the photoconductor drum 109BK ischarged uniformly by the charger 110BK in a dark environment, and thenan electrostatic latent image for black image is formed on thephotoconductor drum 109BK by irradiating light from a light source forblack image in the optical writing unit 111. The development unit 112BKdevelops the electrostatic latent image using black toner, and thenblack toner image is formed on the photoconductor drum 109BK.

The black toner image is transferred to the transport belt 105 at atransfer position of the photoconductor drum 109BK and the transportbelt 105 by a transfer unit 115BK, in which the photoconductor drum109BK and the transport belt 105 may contact or be the closest with eachother. With this transfer, the black toner image is formed on thetransport belt 105. Upon completing the transfer of black toner image,the photoconductor cleaner removes toner remaining on the outer face ofthe photoconductor drum 109BK, and then the photoconductor drum 109BK isdecharged by the decharger 113BK to prepare for a next image formingoperation.

The transport belt 105 transferred with the black toner image by theimage forming unit 106BK is transported to the image forming unit 106M,next to the image forming unit 106B, by rotating the transport belt 105.Similar to the image forming process at the image forming unit 106BK,the image forming unit 106M forms magenta toner image on thephotoconductor drum 109M, and the magenta toner image may besuperimposed and transferred on the black toner image.

The transport belt 105 having the transferred black toner image andmagenta toner image is then transported to the image forming units 106C,106Y. Similar to the image forming unit 106BK, cyan toner image formedon the photoconductor drum 109C, and yellow toner image formed on thephotoconductor drum 109Y may be superimposed and transferred on theblack toner image and magenta toner image, with which the intermediatetransfer image of full color is formed on the transport belt 105.

The sheet 104 stacked in the sheet tray 101 is fed from the top sheet,and the intermediate transfer image formed on the transport belt 105 istransferred on the sheet 104 at a transfer position that the transportbelt 105 and the sheet 104 contact or be the closest with each other inthe transport route, with which an image is formed on the sheet 104. Thesheet 104 formed with the image is transported to a fusing unit 116 tofuse the image on the sheet 104, and then ejected from the image formingapparatus.

In the fusing unit 116, the toner image transferred on the sheet 104 isfused by heat, in which water included in the sheet 104 is vaporizedwhen the sheet 104 is passing through the high temperature fusing unit116, with which the sheet 104 shrinks and therefore the image size onthe sheet 104 ma be come smaller than the image size of original image.When the scanner 302 scans the shrink sheet 104, the scanned imagesmaller than the original image may be generated.

Further, when the duplex printing is conducted, the sheet 104 having thefused image is transported to an inverting route to invert the faces ofthe sheet 104, and then the sheet 104 is transported to the transferposition again. The sheet 104 having the fused image on one face or bothfaces is transported to the scanner 302. Then, the scanner 302 scans oneface or both faces, with which a scanned image, which is an inspectiontarget image, is generated.

A description is given of the inspection apparatus 4 by referring FIG. 3again. The scanned image obtainer 401 obtains the scanned image datagenerated by scanning the sheet face by the scanner 302 in the printengine 3, and inputs the scanned image data as an inspection targetimage to the inspection unit 404. As described above, the master imageprocessing unit 402 obtains the bitmap data input from the enginecontroller 2, and generates a master image as an inspection referenceimage to be compared with the inspection target image. Therefore, basedon the output-target image, the master image processing unit 402 is usedas an inspection reference image generator that generates the masterimage as the inspection reference image to be used for inspecting thescanned images. The generation process of master image by the masterimage processing unit 402 will be described later.

The inspection control unit 403 controls the inspection apparatus 4 as awhole, and each unit in the inspection apparatus 4 is operated under thecontrol of the inspection control unit 403. Further, in an exampleembodiment, the inspection control unit 403 includes, for example, amaster image generation controller 403 a, an image comparison inspectioncontroller 403 b, a threshold determination processing unit 403 c, auser interface (UI) controller 403 d and a range determinationcontroller 403 e as shown in FIG. 3. The inspection unit 404 is used asan image inspection unit that compares the scanned image data, inputfrom the scanned image obtainer 401, and the master image, generated bythe master image processing unit 402, to determine whether a desiredimage forming operation is conducted. The inspection unit 404 may beconfigured with the above mentioned ASIC or the like to compute a greatamount of data with high speed processing.

A description is given of the master image processing unit 402 withreference to FIG. 5. FIG. 5 shows an example block diagram of the masterimage processing unit 402. As shown in FIG. 5, the master imageprocessing unit 402 includes, for example, a binary/multi-valueconverter 421, a resolution level converter 422, a color converter 423and a master image outputting unit 424. The master image processing unit402 can be devised as the specific device 80 (see FIG. 2) devised by acombination of hardware and software such as the ASIC controlled bysoftware. The inspection unit 404 and the master image processing unit402 can be configured using the ASIC as described above. Further, theinspection unit 404 and the master image processing unit 402 can beconfigured using a software module executable by the CPU 10.

The binary/multi-value converter 421 conducts a binary/multi-valueconverting process to a binary format image expressed binary such ascolor/non-color to generate a multi-valued image. The bitmap data isinformation input to the print engine 3. The print engine 3 conducts animage forming operation based on binary format image for each color ofcyan, magenta, yellow, black (CMYK). Because the scanned image data,which is the inspection target image, is a multi-valued image composedof multi-gradient image of the three primary colors of red, green andblue (RGB), a binary format image is initially converted to amulti-valued image by the binary/multi-value converter 421. Themulti-valued image is, for example, an image expressed by 8-bit for eachCMYK.

Further, the print engine 3 conducts an image forming operation based onbinary format image for each of CMYK, and the master image processingunit 402 includes the binary/multi-value converter 421 but not limitedhereto. For example, when the print engine 3 conducts an image formingoperation based on multi-valued image, the binary/multi-value converter421 can be omitted.

The resolution level converter 422 conducts a resolution levelconversion process to match a resolution level of multi-valued imagegenerated by the binary/multi-value converter 421 to a resolution levelof the scanned image data (i.e., inspection target image). Because thescanner 302 generates scanned image data, for example, with theresolution level of 200 dots per inch (dpi), the resolution levelconverter 422 converts a resolution level of multi-valued imagegenerated by the binary/multi-value converter 421 to 200 dpi.

The color converter 423 obtains the image having converted with theresolution level by the resolution level converter 422 and conducts acolor converting process. Because the scanned image data is RGB-formatimage as described above, the color converter 423 converts theCMYK-format image having converted with the resolution level by theresolution level converter 422 to the RGB-format image, with which amulti-valued image of 200 dpi expressed with 8-bit for each of RGB(total 24 bits) for each pixel is generated.

The master image outputting unit 424 outputs the master image, generatedby using the binary/multi-value converter 421, the resolution levelconverter 422 and the color converter 423, to the inspection controlunit 403. Based on the master image obtained from the master imageprocessing unit 402, the inspection control unit 403 instructs theinspection unit 404 to conduct an image comparing process to obtain acomparison result.

Referring back to FIG. 4, the inspection unit 404 compares the scannedimage data and the master image expressed with 8-bit for each of RGB(total 24 bits) as described above for each corresponding pixel, andcomputes difference of pixel values for each of RGB for each pixel.Based on the comparison of the computed difference and a threshold, theinspection unit 404 determines whether a defect occurs to the scannedimage data. Therefore, the inspection unit 404 can function as an imageinspection unit to determine defect of the scanned image data based ondifference of the inspection reference image and the scanned image data.Further, the difference computed for each of pixels can be correlatedfor each of pixel positions and can be configured as a differentialimage.

Further, the difference and the threshold can be compared by theinspection unit 404 as follows. For example, values of differencecomputed for each of pixels are summed for a given area of an image as atotal value, and the total value is compared with the threshold, whichis set to be compared with the total value. The given area for summingthe values of difference of each of pixels is, for example, a 20-dotsquare area. In an example embodiment, therefore, the threshold is avalue set for the total difference value of the given area (hereinafter,defect determination unit area) obtained by summing the differencevalues. Therefore, the inspection unit 404 outputs position informationof the defect determination unit area on an image having a totaldifference value exceeding the threshold, wherein this positioninformation can be used as information indicating the presence of defectin the scanned image data. The position information in the image isdefined by, for example, coordinate information on image.

When comparing the scanned image and the master image, the scanned imageis divided into a plurality of areas as shown in FIG. 22. The inspectionunit 404 superimposes each divided area to a corresponding area of themaster image to compute a difference of pixel value of each pixel suchas difference of density. Further, a position of superimposing thedivided area to the master image is shifted left/right and up/down todetermine a position that the computed difference becomes the smallestand the smallest difference is used as a comparison result. Each one ofthe divided areas shown in FIG. 22 can be used as the above describeddefect determination unit area.

Further, the above described threshold can be provided by registersetting to the inspection unit 404 configured as, for example, ASIC. Theinspection control unit 403, which is configured by executing a programby the CPU 10, writes a threshold, set as shown in FIG. 23, to theregister provided to designate a threshold for the inspection unit 404,with which the above described threshold can be set.

Further, in another method, each pixel is determined as normal or defectbased on a comparison result of the difference computed for each pixeland the threshold, and the count number of pixels determined as defectand the threshold set for the count number are compared.

In the system according to an example embodiment, when settingthresholds used for the image comparing process by the inspection unit404, thresholds matched to inspection precision, which may be desired bya user, can be set easily, and therefore, each of the modules includedin the inspection control unit 403 can be used to determine the abovementioned threshold using each unit of the inspection apparatus 4. Adescription is given of a process of setting the threshold withreference to FIG. 6.

FIG. 6 is a flowchart of process of setting threshold according to anexample embodiment. As shown in FIG. 6, when setting the threshold,under the control of the engine controller 2, the print engine 3conducts a printing operation for images used for setting thresholds(hereinafter, referred to as threshold setting image) (S601). FIGS. 7Ato 7C show examples of threshold setting images according to an exampleembodiment. As for the threshold setting images, FIG. 7A shows referenceimage pattern 701, which is an image having normal image condition notadded artificial defects, and the reference image pattern is used todetermine thresholds. As shown in FIG. 7A, the reference image pattern701 can be drawn and formed in 4 rows in the horizontal direction or theX direction, and 5 lines in the vertical direction or the Y directionfor given color mark. The images of FIG. 7A can be output as a firstimage using the print engine 3 under the control of the enginecontroller 2.

By contrast, FIGS. 7B and 7( c) show threshold setting images preparedby adding a plurality of different artificial defects to the abovedescribed reference image of normal condition. FIG. 7B show imagesprepared by adding artificial defects having different color densitiesto the above described reference image pattern (hereinafter,density-changed defect pattern 702). As shown in FIG. 7B, thedensity-changed defect pattern 702 can be prepared by adding differentartificial defects to each one of marks arranged in the X direction andthe Y direction. The images of FIG. 7B can be output as a second imageusing the print engine 3 under the control of the engine controller 2.

As for the density-changed defect pattern, each mark arranged in the Xdirection is added with artificial defects of different colors, and eachmark arranged in the Y direction is added with artificial defects ofdifferent densities. Therefore, the images of FIG. 7B are images addedwith a plurality of artificial defect having different colors anddensity levels. FIG. 8 shows an example of information referred by theengine control unit 202 of the engine controller 2 when outputting thedensity-changed defect pattern 702 shown in FIG. 7B (hereinafter,density-changed defect pattern information). Further, information of thedensity-changed defect pattern of FIG. 8 can be stored, for example, ina storage included in the engine controller 2 such as the RAM 20, ROM30, HDD 40, and/or an external storage.

In FIG. 8, PC, PM, PY and PK are values indicating colors such as C, M,Y, K for the pattern. As shown in FIG. 8, as for the density-changeddefect pattern information, each pattern arranged in 4 rows in the Xdirection and 5 lines in the Y direction is set with color informationof artificial defects. For example, as a pattern for the firstline/first row, PC is added with d₁, and as for other M, Y, K in thefirst line, the same value of color are added with as artificial defect,in which d₁ is added to PM at the second row, to PY at the third row,and to PK at the fourth row, with which artificial defects having colorsdifferent from the original pattern can be prepared.

Further, as shown in FIG. 8, adding values can be changed such as +d₁,+d₂, +d₃ . . . in the Y direction, in which the greater the value of nof d_(n), the greater the density, which means, in the Y direction,color density becomes thicker by adding values of artificial defects.The change of density is indicated in FIG. 7B by using line patternssuch as dot line, dashed line, or the like.

When outputting the density-changed defect pattern shown in FIG. 7B, theengine control unit 202 obtains settings for a range for changingdensity, and determines a value of d_(n) shown in FIG. 8 based on theobtained settings for the range. The settings for the range may includevalues that may be set for the engine control unit 202 in advance, orset manually by a user when outputting the density-changed defectpattern.

The d_(n) can be obtained using the following formula (I) by setting thelower limit d_(m) and the upper limit d_(M) for the settings of therange.d _(n) =d _(m)+¼(d _(M) −d _(m))×n  (1)

Based on the computation using the above formula (1), the range of fromd_(m) to d_(M) can be divided equally, for example, by five values of d₁to d₅, and can be used as the adding values of density. The d_(m) andd_(M) can be provided as setting values as shown in FIG. 24 according toan example embodiment.

FIG. 7C show images prepared by adding artificial defects havingdifferent line width to the above described reference image pattern(hereinafter, width-changed defect pattern 703). Similar to thedensity-changed defect pattern, as shown in FIG. 7C, the width-changeddefect pattern 703 can be prepared by adding different artificialdefects to each one of marks arranged in the X direction and the Ydirection. Similar to the images of FIG. 7B, the images of FIG. 7C areimages added with a plurality of artificial defect different in colorand width. The images of FIG. 7C can be output as a third image usingthe print engine 3 under the control of the engine controller 2. Similarto the density-changed defect pattern 702, as for the width-changeddefect pattern 703, each mark arranged in the X direction is added withartificial defects of different colors, and each mark arranged in the Ydirection is added with artificial defects of different width.

Similar to the density-changed defect pattern, the engine control unit202 changes width of artificial defects within a set range for changingwidth of artificial defects shown in FIG. 7C. The range of changingwidth can be computed using the above formula (I) as d_(n) of width ofartificial defects. Further, the engine control unit 202 stores thecomputed d_(n) to be used for a later processing.

Further, in an example embodiment, the engine control unit 202 cangenerate bitmap data used for an image forming operation of the patternsshown in FIG. 7A to FIG. 7C, but the DFE 1 can generate bitmap data.

In the process at S601, the engine controller 2, the print engine 3 andthe inspection apparatus 4 respectively conduct the above describedoperations, in which the engine controller 2 transmits the bitmap datato the inspection apparatus 4, and data of the scanned image, generatedin the print engine 3 by scanning the output sheet using the scanner302, is input to the inspection apparatus 4. Then, when setting thethresholds, based on the bitmap data input from the engine controller 2,the inspection apparatus 4 generates a master image based on bitmap dataof the first image (S602 a), and selects and obtains data of scannedimage of the second image and the third image (S602 b).

In the process at S602 a, among bitmap data of the first, second andthird images input from the engine controller 2, the master imagegeneration controller 403 a of the inspection control unit 403 controlsthe master image processing unit 402 to generate a master image only forthe first image. The master image is used as the inspection referenceimage as described above. The master image is also referred to as anormal reference image used for inspection, and the normal referenceimage is used as the inspection reference image for the preparing theabove described threshold setting image.

Further, in the process at S602 b, the image comparison inspectioncontroller 403 b of the inspection control unit 403 controls the scannedimage obtainer 401 to discard the scanned image data of the first imagefrom the scanned image data of the first, second and third images inputfrom the print engine 3, and obtains the scanned image of the secondimage and the third image. The scanned image data is image data obtainedby scanning the above described threshold setting image, wherein scannedimage data is also referred to as defect scanned image.

Then, the image comparison inspection controller 403 b of the inspectioncontrol unit 403 controls the inspection unit 404 to compare the abovedescribed master image of first image and the scanned image of thesecond and third images (image comparing process) to compute the abovedescribed difference for each of the second image and the third image toobtain a differential image (S603).

Upon obtaining the differential image for the second image and the thirdimage with respect to the master image, as explained with reference toFIGS. 7A to 7C, the threshold determination processing unit 403 c of theinspection control unit 403 computes a threshold to detect an artificialdefect artificially added in each of marks arranged in rows and lines asdefect (S604). In the process of S604, as shown in FIG. 9, thresholdsuch as th11, th12 . . . can be computed for each of marks arranged in 4rows in the X direction and 5 lines in the Y direction. In S604, basedon the difference generated for each one of a plurality of artificialdefects having different colors and levels, a threshold to be used fordetermining each one of the plurality of artificial defects as defectcan be computed, and the each computed threshold is referred to asdiscrete threshold. Further, information shown in FIG. 9 can be stored,for example, in a storage included in the inspection unit 404 such asthe RAM 20, ROM 30, HDD 40, and/or an external storage.

FIG. 9 shows an example of a table having discrete thresholds. In anexample embodiment, a discrete threshold is set for each mark includedin the second image and the third image. Therefore, the table shown asFIG. 9 can be generated for each of the second image and the thirdimage.

A description is given of a detail of S604 (FIG. 6) with reference toFIG. 10. As shown in FIG. 10, the threshold determination processingunit 403 c sets a starter threshold (S1001) at first. The starterthreshold is a threshold that any types of defect are not extracted asdefect, which means that even if a total difference value for the defectdetermination unit area is great, a value greater than the totaldifference value for the defect determination unit area is set as thestarter threshold, with which no defect is determined as defect.

Upon setting the starter threshold, the threshold determinationcontroller 403 a of the inspection control unit 403 controls theinspection unit 404 to conduct a defect determination process based onthe set threshold (S1002). In S1002, a defect determination process isconducted for an entire image by conducting a defect determinationprocess for each defect determination unit area. In S1002, as describedabove, in the defect determination process, a total difference and athreshold are compared to determine whether each defect determinationunit area is defect.

Then, the inspection control unit 403 stores coordinates of areas on animage displaying each mark as shown in FIG. 11 in advance, and comparescoordinates of determination unit area determined as defect andcoordinates stored in advance to determine which mark is determined asdefect. Further, information shown in FIG. 11 can be stored in advancein the inspection control unit 403 or can be input from the enginecontrol unit 202 or other device each time when the threshold settingprocess is conducted.

If each area displaying a mark is determined as current defect based onthe determination result of S1002 (S1003: YES), the thresholddetermination processing unit 403 c registers or sets a currently-usedthreshold as a threshold for the area determined as current defect tothe table shown in FIG. 9 (S1004). With this processing, each discretethreshold such as th11, th12 and so on shown in FIG. 9 can beregistered.

Upon completing S1004, the threshold determination processing unit 403 cchecks whether a threshold is set for all of areas (S 1005). If thethreshold is set for all of areas as shown in FIG. 9 (S1005: YES), theprocess ends. By contrast, if no area is determined as current defectwhen S1002 is conducted (S1003: NO), or if the threshold is not yet setfor all of areas (S1005: NO), the threshold determination processingunit 403 c changes a value of the threshold to increase the probabilityto be determined as defect (S1006), and repeats the process from S1002.

In an example embodiment, the threshold determination processing unit403 c can change values of threshold gradually to increase theprobability to be determined as a defect, and repeats the defectdetermination process until all of areas are determined as defect. Withthis processing, as explained with reference to FIGS. 7B and 7C,thresholds matched to an actual defect determination process can bedetermined based on thresholds used for extracting various artificialdefects having different levels. Further, in an example embodiment,because the defects can be determined based on the scanned image datagenerated by the scanner 302, thresholds matched to the images scannedreal time by the scanner 302 can be set.

Upon completing the process of S604, the UI controller 403 d controls adisplay unit to display a graphical user interface (GUI), which is usedby a user to set a threshold, and the inspection control unit 403receives a selection result input by a user's operation (S605). The GUIdisplayed in S605 is referred to as a threshold selection screenhereinafter, and FIGS. 12A and 12B show examples of threshold selectionscreens. The threshold selection screens shown in FIGS. 12A and 12B canbe displayed on a display unit such as the LCD 60 connected to theinspection apparatus 4. FIG. 12A shows an initial screen of GUIdisplayed in S605, which means a screen before a user's selectionoperation.

As shown in FIG. 12A, the threshold selection screen displays images ofthe density-changed defect pattern and the width-changed defect patterndescribed with reference to FIGS. 7B and 7C. These images can bedisplayed using, for example, the second image and the third imageobtained by the scanned image obtainer 401. The user can select one ormore marks to be identified as defect on the screen shown in FIG. 12A.

When selecting the mark on the screen shown in FIG. 12A, the useroperates the screen, but the mark is selected by looking the outputsheet (i.e., not selected on the screen), in which the user candetermine the defect based on the defect actually output on the sheet.FIG. 12B shows an example screen when images to be identified as defectare selected by the user. As shown in FIG. 12B, the mark selected by theuser is displayed on the screen with high-lighted condition such asencircling frame.

When the mark is selected as described above, the UI controller 403 dobtains the selection result, and the threshold determination processingunit 403 c can set a threshold to detect each mark as defect byreferring the table shown in FIG. 9. Specifically, when the UIcontroller 403 d receives the user's selection at S605, the thresholddetermination processing unit 403 c extracts a discrete threshold,corresponding to the defect selected by the user shown in as shown inFIG. 12B, from the table shown in FIG. 9. In this process, the UIcontroller 403 d recognizes one or more defects selected by an operationto the screen shown in FIG. 12A by a user.

Specifically, when one or more marks are selected as defect as shown inFIG. 12B, the threshold determination processing unit 403 c obtainsinformation of arrangement position of the selected defect on the image,and identifies the arrangement in X direction and the arrangement in Ydirection indicated in the table of FIG. 9. Then, the thresholddetermination processing unit 403 c extracts information of thresholdcorresponding to the arrangement position of the selected defect such asth11, th21 and so on from the table shown in FIG. 9.

Upon extracting the discrete thresholds for the selected defects (FIG.12B) from the table of FIG. 9, the threshold determination processingunit 403 c determines a finally-set threshold based on the extracteddiscrete thresholds (S606). In S606, among the extracted discretethresholds corresponding to the marks selected by the user asto-be-determined as defect, the threshold determination processing unit403 c determines one of the discrete thresholds as the finally-setthreshold, in which a discrete threshold having the strictest thresholdis determined as the finally-set threshold. When the strictest thresholdis set as the finally-set threshold, the greater number of marks can bedetermined as defect. The threshold determined with this process can bestored as the threshold setting as shown in FIG. 23, and when theinspection unit 404 conducts an inspection by comparing images, athreshold can be provided to the inspection unit 404 by writing thethreshold as a register value by the inspection control unit 403.

Upon determining the finally-set threshold, the threshold determinationprocessing unit 403 c determines whether re-adjustment is required basedon the user's operation (S607), in which the UI controller 403 obtainsan operation instruction by the user. In S607, the thresholddetermination processing unit 403 c controls a display unit such as theLCD 60 connected to the inspection apparatus 4 to display a screen forselecting whether the re-adjustment is required, and determines whetherthe re-adjustment is required based on the user's operation to thescreen.

If the re-adjustment is not required (S607: NO), the thresholddetermination processing unit 403 c ends the process. By contrast, ifthe re-adjustment is required (S607: YES), the threshold determinationprocessing unit 403 c instructs the engine controller 2 to repeat thesteps from S601 and controls the inspection apparatus 4, in which asdescribed above, the inspection control unit 403 designates a range ofchanging density and/or width of the density-changed defect pattern orthe width-changed defect pattern. Specifically, the thresholddetermination processing unit 403 c can designate d_(n) for the markhaving the maximum value d_(M) and the minimum value d_(m) for eachdiscrete threshold extracted at S605.

As described above, the d_(n) computed for each mark can be stored inthe storage included in the engine controller 2 such as the RAM 20, ROM30, HDD 40, and/or the external storage. Therefore, the thresholddetermination processing unit 403 c can designate “d_(n)” for each ofthe density-changed defect pattern and the width-changed defect patternto the engine control unit 202 by only notifying a position in the Ydirection of a mark corresponding to the above described maximum valueand minimum value.

Further, at S605, a discrete threshold can be extracted for each of thedensity-changed defect pattern and the width-changed defect pattern.Therefore, the threshold determination processing unit 403 c designatesd_(n) for a mark corresponding to the maximum value and the minimumvalue of each discrete threshold extracted at S605 for each of thedensity-changed defect pattern and the width-changed defect pattern.

When the process of S601 is to be conducted repeatedly, the mark addedwith the artificial defect corresponding to the maximum value and theminimum value of the discrete threshold, extracted by the process atS605 by already conducting the threshold setting process once, can beformed as the density-changed defect pattern and the width-changeddefect pattern. By conducting the process of FIG. 6 for the second imageand the third image, the threshold can be set more precisely.

In the system of an example embodiment, images displaying defects havingchanged the defect level step-wisely as shown in FIGS. 7B and 7C areprepared. By conducting the defect determination process by changing thethresholds step-wisely, discrete thresholds that can detect each ofdefects having step-wisely changed defect levels can be obtained. Then,the user checks a sheet printed with a given pattern with eyes to selectone or more marks to be determined as defect, and determines thefinally-set threshold based on the discrete threshold correlated to theselected marks. With this processing, when the image inspection isconducted based on a comparison result obtained by comparing an imagegenerated by scanning an image output by an image forming operation anda master image, the setting of threshold used for determining the defectcan be conducted easily and preferably based on the comparison result.

In the above described example embodiment, when repeatedly conductingthe adjustment of threshold, levels of artificial defects are changeddepending on a selection result by a user, but when the adjustment ofthreshold is initially activated, the level of artificial defect isrequired to be determined without the user's selection. In this case,depending on the capability of the scanner 302 of the print engine 3 andthe conditions of the scanner 302, the levels of defects that can beidentified may become different.

For example, when identifying a defect of stripe shape, a stripe havinga narrow width cannot be scanned depending on a scan-able resolutioncapability of the scanner 302. Further, when identifying a defect ofdensity change, if a level of density change from a normal condition issmall, for example, if the density change is a pale appearance,depending on a density resolution capability of the scanner 302, thescanned image cannot be distinguished between a defect condition and anormal condition, because pixel values of the scanned image data may notbe different between the defect condition and the normal condition.

Therefore, if the images shown in FIGS. 7B and 7C are output when theadjustment of threshold is initially activated and the image include adefect having a level that cannot be detected by the scanner 302, and auser selects this undetectable defect, a preferable threshold may not beset. Therefore, in the system according to an example embodiment, acalibration is conducted to limit a range of defect levels added as thedensity-changed defect pattern and/or the width-changed defect pattern.A description is given of a calibration process according to an exampleembodiment.

In the calibration process according to an example embodiment, the printprocessing unit 301 outputs a calibration-use image, the scanner 302generates scanned image of the calibration-use image, and the inspectionapparatus 4 conducts a defect determination process for thecalibration-use image similar to the normal defect determinationprocess, with which a range of defect that can be identified or detectedby the scanner 302 can be determined. With this processing, the value ofd_(m) and d_(M) shown in FIG. 24 can be determined and set. Adescription is given of calibration-use image according to an exampleembodiment with reference to FIG. 13.

FIG. 13 shows an example of calibration-use image, which mean the imageshown in FIG. 13 can be used as range determination image. As shown inFIG. 13, the calibration-use image includes, for example, a stripedefect pattern 501, a dot defect pattern 502 and a density defectpattern 503. The stripe defect pattern 501 includes stripe defectpatterns of CMYK and white (W) by arranging from bold width to thinwidth. By using this pattern, it can confirm a level of stripe defectpattern that can be detected as defect based on the levels of width ofstripe.

Further, as shown in FIG. 13, the stripe defect patterns of W areformed. This stripe defect pattern of W can be used as white stripepatterns occurring when a background color is non-white. Therefore, abackground color of an entire calibration-use image shown in FIG. 13 maybe set non-white, or a background color corresponding only to the Wpattern in the stripe defect pattern 501 may be set non-white.

The dot defect pattern 502 includes dot defect patterns of K and W byarranging from large to small dots. By using this pattern, it canconfirm levels of dot defect pattern that can be detected as defectbased on the levels of dot size. Further, similar to the W pattern ofthe stripe defect pattern 501, the white (W) dot defect pattern isformed in the dot defect pattern 502. Therefore, a background color ofan entire calibration-use image shown in FIG. 13 may be set non-white,or a background color corresponding only to the W pattern in the dotdefect pattern 502 may be set non-white.

The density defect pattern 503 includes density defect patterns of Khaving a given size and a shape such as tetragon (e.g., square) byarranging from thick to pale colors, that is from black to grey towhite. By using this pattern, it can confirm what level of densitychange can be detected as defect based on density. Further, in FIG. 13,the density change is expressed by types of line such as cross-hatchingand slanted line.

Further, in FIG. 13, K and W dot defect are used as the dot defectpattern 502, and K tetragon is used as the density defect pattern 503.Further, dot defects of CMY and a plurality of colors, and densitydefects of CMY and a plurality of colors can be used.

FIG. 14 shows an example of information used to determine the level ofdefect that can be used effectively (hereinafter, calibration-useinformation). The calibration-use information can be prepared byanalyzing a defect determination result of the calibration-use imageshown in FIG. 13. As shown in FIG. 14, the calibration-use informationcorrelates defect identification (ID), coordinates, defect type anddefect detail. The defect ID is used to identify each one of defects.The coordinates indicate a position of each defect displayed on thecalibration-use image of FIG. 13. The defect type indicates the types ofeach defect. The defect detail indicates a detail of each defect.

For example, as for the calibration-use information corresponding to thestripe defect pattern 501, information of “stripe for cyan (C)” and“width of 30 dots” indicates that a stripe is defect of C and its width,and these information is registered. Further, as for the calibration-useinformation corresponding to the dot defect pattern 502, information of“dot” and “diameter 100 dots” indicates a dot defect and dot defectdiameter, and these information is registered. Further, as for thecalibration-use information corresponding to the density defect pattern503, information of “density” and “C₂₁, M₂₁, Y₂₁, K₂₁” indicates densitydefect and density of each color, and these information is registered.

Further, the coordinates information shown in FIG. 13 can usecoordinates of a center position of an area displaying each defect butnot limited hereto. The coordinate information can use coordinates oftop left position of an area displaying each defect, or the coordinateinformation can use coordinates of top left position and bottom rightposition of an area displaying each defect to identify the area.

A description is given of a calibration process according to an exampleembodiment with reference to a flowchart shown in FIG. 15. As shown inFIG. 15, in the calibration process, under the control of the enginecontroller 2, the print engine 3 conducts a printing operation for thecalibration-use image shown in FIG. 13 (S1501).

When the calibration-use image is printed, in the inspection apparatus4, under the control of the range determination controller 403 e of theinspection control unit 403, the master image processing unit 402generates a master image, and the scanned image obtainer 401 obtainsscanned image for the calibration-use image from the scanner 302(S1502). The scanned image of the calibration-use image can be used as arange determination scanned image. The master image with respect to thecalibration-use image of FIG. 13 is a blank image, which is a backgroundcolor of sheet. Therefore, when the calibration-use image is printed,the master image can be generated as follows. For example, the bitmaptransmitter 203 outputs blank bitmap data, and the master imageprocessing unit 402 generates a master image by conducting a normaloperation using the blank bitmap data, or the range determinationcontroller 403 e notifies the above blank color information to themaster image processing unit 402, and the master image processing unit402 generates the blank master image.

When the master image and the scanned image data are obtained by theinspection apparatus 4, the range determination controller 403 econtrols the inspection unit 404 to compare the master image and thescanned image (image comparing process) to compute a difference betweenthe master image and the scanned image, and obtains a differential image(S1503). When the differential image for the calibration-use image withrespect to the blank master image is obtained, the range determinationcontroller 403 e conducts a defect determination using the settableupper limit and lower limit of threshold (S1504). Further, at S1503 andS1504, the defect determination is conducted for each divided area,prepared by dividing an image into a plurality of areas, as explainedwith reference to FIG. 22.

The above described settable upper limit and lower limit of thresholdare the upper limit and the lower limit of the threshold applied to atotal difference summed for each defect determination unit area asdescribed above. The upper limit is a value for the broadest allowablerange, which means the number of defects not determined as defectbecomes the greatest. Further, the lower limit is a value for thenarrowest allowable range, which means the number of defects determinedas defect becomes the greatest.

As described above, the inspection unit 404 compares the set thresholdand the total difference for each defect determination unit area, andoutputs coordinate information of an area having the total differenceexceeding the threshold. Therefore, the range determination controller403 e can recognize a defect type and defect detail determined as defectby referring the calibration-use information shown in FIG. 14.

FIGS. 16A and 16B schematically show defect determination results usingthe above described upper limit and the lower limit. FIG. 16A showspatterns determined as defect using the upper limit of the thresholdcorresponding to the broadest allowable range, and three patternsencircled by dashed lines are determined as defect.

In a case of FIG. 16A, although the threshold of the broadest allowablerange is applied, patterns 501 a to 501 c are determined as defect.Therefore, even if marks corresponding to the pattern 501 b and pattern501 c are selected as allowable defect on the screen shown in FIGS. 11Aand 11B by a user, such user's instruction cannot be input as aneffective instruction, which means the threshold set by the selectionresult of the user is out of the settable range.

Therefore, range determination controller 403 e obtains defect detailinformation corresponding to the pattern 501 c of FIG. 16A, anddetermines d_(M) based on the defect detail information, wherein d_(M)is the upper limit of the range used for changing defect levelsdescribed with FIG. 8 (S1505). In S1505, range determination controller403 e can function as a defect range determiner to determine a range oflevels of a plurality of artificial defects having different levels,wherein the plurality of artificial defects having different levels canbe displayed as the density-changed defect pattern and the width-changeddefect pattern.

Further, d_(M) can be determined by referring the pattern 501 c of FIG.16A, which is a pattern having the smallest level of defect amongpatterns determined as defect using the threshold having the broadestallowable range. Further, d_(M) can be determined by referring apattern, which is next to the pattern 501 c and having the greatestdefect level among patterns determined not as defect using the thresholdhaving the broadest allowable range.

In a case of FIG. 16B, although a threshold of the narrowest allowablerange is applied, patterns 501 d to 501 h are not determined as defect.Therefore, even if marks corresponding to the patterns 501 d to pattern501 h are selected as defect on the screen shown in FIGS. 11A and 11B,such user's instruction cannot be input as an effective instruction,which means thresholds set by the selection result of the user is out ofthe settable range.

Therefore, the range determination controller 403 e obtains defectdetail information corresponding to the pattern 501 d of FIG. 16B, anddetermines d_(m) based on the defect detail information, wherein d_(m)is the lower limit of the range used for changing defect levels asdescribed with FIG. 8 (S1505). Further, d_(m) can be determined byreferring the pattern 501 d of FIG. 16B, which is a pattern having thegreatest levels of defect among patterns determined not as defect usingthe threshold having the narrowest allowable range. Further, d_(m) canbe determined by referring a pattern, which is next to the pattern 501 dand having the smallest defect level of among patterns determined asdefect using the threshold having the narrowest allowable range.

Further, as explained with reference to FIG. 13, because thecalibration-use image includes the stripe defect pattern 501, the dotdefect pattern 502 and the density defect pattern 503, the defectdetermination range shown in FIG. 16A and FIG. 16B can be obtained foreach defect pattern. Further, as shown in FIG. 14, defect detailinformation is registered with information corresponding to each defectpattern such as width of 30 dots, diameter of 100 dot, and C₂₁, M₂₁,Y₂₁, K₂₁.

Therefore, the range determination controller 403 e obtains values ofd_(m) and d_(M) by referring defect detail information for each type ofdefect at S1505. For example, as for d_(m) and d_(M) corresponding tothe width-changed defect pattern of FIG. 7C, information correspondingto the stripe defect pattern 501, and information corresponding to thedot defect pattern 502 can be obtained from the defect detailinformation shown in FIG. 14. Further, as for d_(m) and d_(M)corresponding to the density-changed defect pattern of FIG. 7B,information corresponding to the density defect pattern 503 can beobtained.

Further, defect detail information corresponding to the density defectpattern 503 of FIG. 14 is information indicating density of the patternitself, but not information indicating density change from thebackground color. Therefore, when the range determination controller 403e obtains d_(m) and d_(M) information based on the defect detailinformation corresponding to the density defect pattern 503, theinspection control unit 403 obtains a difference between densityinformation indicated in defect detail information and densityinformation of the background color.

Upon determining the values of d_(m) and d_(M) in this process as thesetting value shown in FIG. 24, the range determination controller 403 etransmits the determined values to the engine controller 2 (S1506), andthe process ends. With this processing, the values of d_(m) and d_(M)can be input to the engine control unit 202. Therefore, when the enginecontrol unit 202 generates the images of FIGS. 7B and 7( c) forconducting a threshold determination process, the density-changed defectpattern and the width-changed defect pattern can be generated preferablywithout meaningless selection by a user.

In an example embodiment, as shown in FIGS. 7B and 7C, thedensity-changed defect pattern and the width-changed defect pattern areused. Further, as shown in FIG. 17, when patterns displaying dot defectshaving different levels for each mark are used, defect detailinformation corresponding to the dot defect pattern 502 can be usedeffectively when obtaining d_(m) and d_(M).

Further, in the above described example embodiment, when setting thethresholds, for example, a printing operation of images shown in FIGS.7A to 7C is conducted. With this configuration, for example, a processof changing a range of to-be-set threshold (e.g. S607 in FIG. 6) can beconducted repeatedly. If the process of changing a range of threshold isnot required, bitmap data of images shown in FIG. 7A is input to themaster image processing unit 402, and a known scan-use chart having theimages similar to the images shown in FIGS. 7B and 7C can be scanned bythe scanner 302 of the print engine 3, with which the above describedoperation can be conducted.

Further, in the above described example embodiment, as shown in FIGS.12A and 12B, the second image and the third image are displayed on ascreen, from which a user can select marks intuitively based on visualinformation displayed on the screen but not limited hereto. For example,a user can select marks from a list shown in FIG. 18, wherein the listincludes position information of marks in the X direction and the Ydirection, which may be indicated as text information.

Further, in the above described example embodiment, as shown in FIGS.7B/7C and FIGS. 12A/12B, a plurality of density-changed defect patternsand width-changed defect patterns are arranged and displayed on thescreen with a given order corresponding to color and levels ofartificial defects set for each mark, with which a user can easilyselect an allowable defect in view of the level of artificial defects.Further, a plurality of density-changed defect patterns and a pluralityof width-changed defect patterns can be arranged and displayed on thescreen randomly for color and levels of artificial defects (i.e., notarranged with a given order), in which a user can select marks withoutpreconception.

Further, as explained with reference to FIGS. 7B and 7C, in an exampleembodiment, the density-changed defect patterns and the width-changeddefect patterns can be reproduced using a plurality of artificialdefects having different levels for each of cyan, magenta, yellow andblack (CMYK). Because of human perception on colors may differ for eachperson, the level of artificial defects that can be allowed or cannot beallowed for each one of colors may be different for each person.

For example, as for a relatively pale color such as Y, one user mayallow a mark corresponding to PY+d₄ shown in FIG. 8 (i.e., only a markcorresponding to PY+d₅ is selected as to-be-determined defect) while thesame user may select marks corresponding to from PK+d₁ to PK+d₅ (i.e.,all of marks shown in FIG. 8) as the to-be-determined defect for K. Inthis case, a threshold set for the mark corresponding to PK+d₁ becomesthe strictest value. If this strictest value is applied, the defect of Ythat the user determines as allowable may be determined as defect.

In this case, the inspection unit 404 can set thresholds step-wisely toenhance the user's convenience. Specifically, the finally set thresholdmay include a first threshold and a second threshold, in which the firstthreshold is set to determine defect without a confirmation of a user,and the second threshold is set to determine defect based on a selectionof a user.

In this case, at S605 (FIG. 6), the threshold determination processingunit 403 c extracts the strictest value as a threshold corresponding tothe selected mark for each artificial defect of each of colors, that isfor each of rows in the table shown in FIG. 9. Then, among thethresholds extracted for each of colors, the threshold determinationprocessing unit 403 c sets a value having a broadest allowable range asthe first threshold, with which a smaller number of defects aredetermined as defect, and sets the strictest value as the secondthreshold, with which a greater number of defects are determined asdefect.

In this processing, if a defect is determined as defect even if thethreshold having the broadest allowable range is applied, a user maydetect the same defect as defect by visual confirmation with a higherprobability, therefore the defect is determined as defect without theconfirmation by the user. Further, if a defect is determined as defectwhen the threshold having the narrowest allowable range is used, it isnot clear whether the user may detect the same defect as defect byvisual confirmation, therefore the defect is determined as defect basedon the confirmation by the user, with which the defect determinationprecision can be enhanced.

Further, when the setting of threshold is conducted repeatedly asexplained with reference for S607 (FIG. 6), the threshold determinationprocessing unit 403 c can designate the values of d_(n) such as d_(m)and d_(M) of d_(n) as the values corresponding to the first thresholdand the second thresholds.

Further, in the above described example embodiment, as explained withreference to FIGS. 12A/12B and S605 (FIG. 6), a mark is selected uponthe visual confirmation of artificial defects by the user, with whichthe inspection apparatus 4 can determine the finally-set threshold basedon the threshold corresponding to the selected mark. With thisconfiguration, the allowable level of defect determination can be seteasily based on the user's visual confirmation.

Further, in the above example embodiment, as shown in FIG. 1, the DFE 1,the engine controller 2, the print engine 3 and the inspection apparatus4 are separate apparatuses with each other. The DFE 1, the enginecontroller 2 and the print engine 3 shown in FIG. 1 can be included inimage forming apparatuses such as printers, which are not image formingapparatuses for commercial printing machines such as productionprinters.

For example, as shown in FIG. 19A, the inspection apparatus 4 can beconnected to a printer having the DFE 1, the engine controller 2 and theprint engine 3. Further, as shown in FIG. 19B, a printer having the DFE1, the engine controller 2, the print engine 3 and the inspectionapparatus 4 can be configured as one printer.

Further, in the above example embodiment, the DFE 1, the enginecontroller 2, the print engine 3 and the inspection apparatus 4 areconnected with each other via a local interface such as universal serialbus (USB), peripheral component interconnect express (PCIe) or the liketo configure the system. However, the inspection apparatus 4 is notrequired to be placed at the same site of the DFE 1, the enginecontroller 2 and the print engine 3, but the inspection apparatus 4 canbe provided as an application for the system, for example, via anetwork.

FIG. 20 shows one example configuration that the function of theinspection apparatus 4 is provided via the network, in which the enginecontroller 2 and the print engine 3 may be connected to the inspectionapparatus 4 via a public line 5 such as the Internet. The enginecontroller 2 and the print engine 3 can transmit information to theinspection apparatus 4 via the public line 5. Further, the inspectionapparatus 4 can transmit an inspection result to the engine controller 2via the public line 5. In this configuration, the inspection apparatus 4is not required at a user site, with which an initial cost of the usercan be reduced.

Further, in the configuration shown in FIG. 20, the user cannot controlthe inspection apparatus 4 directly because the function of theinspection apparatus 4 is provided via the network. In thisconfiguration, the screens shown in FIGS. 12A/12B and FIG. 13 and otherscreens for controlling the inspection apparatus 4 can be displayed onan information processing apparatus such as a personal computer (PC)connectable to the network via a web browser, with which the user canuse the system similar to the above example embodiment.

Further, in the above example embodiment, the first image, the secondimage and the third image are formed on different sheets, but notlimited hereto. For example, the first image, the second image, and thethird image can be formed on the same sheet, in which the master imageprocessing unit 402 generates a master image by extracting an areadisplaying the first image, and further, the scanned image obtainer 401extracts an area displaying the second image and the third image fromthe scanned image, and uses the extracted area as the scanned image datafor the inspection target.

Further, in the above example embodiment, the levels of artificialdefect can be changed by changing the defect density and/or defect range(e.g., width of defect), but not limited thereto. For example, otherparameters of image can be used and changed as required. Further, in theabove example embodiment, each parameter can be changed separately, butparameters can be changed with some combinations.

Further, in the above described example embodiment, the calibrationprocess is conducted by printing a sheet displaying only thecalibration-use image shown in FIG. 13 but not limited hereto. Forexample, the calibration-use image and other image scanned for otherprocess can be formed on the same sheet. For example, a calibrationprocessing for an optical sensor converting optical information toelectrical signals may be conducted for adjustment of the scanner 302 toscan document effectively.

The calibration processing for the optical sensor is a process to matchdocument color, which is a scan target, and image color generated byscanning the document color. For example, a measurement pattern isprinted on a print sheet, and a scan result of the pattern andseparately prepared reference value are compared to adjust scanproperties of the optical sensor. Therefore, as shown in FIG. 21, theabove described calibration-use image and the measurement pattern forcalibration processing of the optical sensor can be printed on the samesheet.

FIG. 21 shows a sheet displaying images (hereinafter, multi-adjustmentimage) including, for example, a measurement pattern 511 for calibrationprocessing of the optical sensor, and the calibration-use image 512. Asshown in FIG. 21, the multi-adjustment image displays the measurementpattern 511 for the calibration processing of the optical sensor, thecalibration-use image 512, and a positioning mark 513 for positioning asheet.

The measurement pattern 511 for the calibration processing of theoptical sensor is an image arranging color patches having various colorsand various densities, and the calibration processing of the opticalsensor is conducted based on a scan result of each color patch andstored-density information for each color patch (hereinafter, colorpatch information). Therefore, similar to the above describedcalibration-use information, the color patch information correlatescoordinate information indicating a position on the sheet andinformation indicating density of each color patch.

When the calibration pattern for the optical sensor and thecalibration-use image are printed on the same sheet, an image formingoperation can be conducted one time and a scanning operation can beconducted one time, with which an adjustment time required for theapparatus can be shortened. Further, when the calibration pattern forthe optical sensor and the calibration-use image are printed on the samesheet, the calibration processing of the optical sensor is preferablyconducted at first and then the calibration process using thecalibration-use image is conducted, with which the calibration effectcan be enhanced.

Further, the calibration-use image of FIG. 13 may be preferably disposedwith a positioning mark such as the positioning mark 513 shown in FIG.21, and the calibration process using the calibration-use image ispreferably conducted after conducting the positioning, with whichdeviation between coordinate information of calibration-use information(FIG. 14) and coordinate information of the scanned image can bereduced, in particular prevented, with which a preferable calibrationeffect can be obtained.

Further, in the above example embodiment, when the thresholddetermination process is conducted, the modules used for the normalinspection process such as the master image processing unit 402, theinspection unit 404 or the like can be controlled by the master imagegeneration controller 403 a and the image comparison inspectioncontroller 403 b, and the threshold determination processing unit 403 cand the UI controller 403 d can be operated based on informationobtained by the control, with which the modules can be collectivelyfunctioned as a threshold determiner.

Similarly, when the defect range determination process is conductedunder the control of the range determination controller 403 e, themodules used for the normal inspection process such as the master imageprocessing unit 402, the inspection unit 404 or the like can becontrolled by the range determination controller 403 e, with whichtheses modules can be collectively functioned as a defect rangedeterminer.

With this configuration, the configuration of apparatus can besimplified by using each module effectively. Further, because the sameor similar modules used for the normal inspection process can be usedfor the threshold determination process and the defect rangedetermination process, these process can be conducted effectively, butthe configuration is not limited hereto. For example, a master imagegeneration module and an image comparison inspection module specificallyemployed for the threshold determination process and the defect rangedetermination process can be provided.

In this case, an inspection reference image generation unit thatgenerates an inspection reference image having a normal image conditionto be used for determining a given threshold for the image inspection,and an image comparison inspection unit that computes a differencebetween the scanned image of the threshold setting image and theinspection reference image can be provided.

Further, in the above example embodiment, the threshold determinationprocessing unit 403 c and the UI controller 403 d are configured in theinspection control unit 403, but the configuration is not limitedhereto. For example, a specific module for the threshold determinationprocessing unit 403 c and a specific module for the UI controller 403 dcan be provided separately from the inspection control unit 403.

Further, in the above example embodiment, one module such as the rangedetermination controller 403 e controls the process of S1502 to S1505 ofFIG. 15, but the configuration is not limited hereto. For example, eachof S1502 to S1505 can be conducted using different modules or some ofthe process of S1502 to S1505 can be collectively controlled by onemodule, in which the modules can collectively function as the defectrange determiner.

In the above example embodiment, an image inspection is conducted bycomparing an image obtained by scanning an image output by an imageforming operation and a master image, and the setting of thresholds usedfor determining defect can be conducted easily and preferably based on acomparison result of images.

The present invention can be implemented in any convenient form, forexample using dedicated hardware, or a mixture of dedicated hardware andsoftware. The present invention may be implemented as computer softwareimplemented by one or more networked processing apparatuses. The networkcan comprise any conventional terrestrial or wireless communicationsnetwork, such as the Internet. The processing apparatuses can compromiseany suitably programmed apparatuses such as a general purpose computer,personal digital assistant, mobile telephone (such as a WirelessApplication Protocol (WAP) or 3G-compliant phone) and so on. Since thepresent invention can be implemented as software, each and every aspectof the present invention thus encompasses computer softwareimplementable on a programmable device.

The computer software can be provided to the programmable device usingany storage medium, carrier medium, carrier means, or digital datacarrier for storing processor readable code such as a flexible disk, acompact disk read only memory (CD-ROM), a digital versatile disk readonly memory (DVD-ROM), DVD recording only/rewritable (DVD-R/RW),electrically erasable and programmable read only memory (EEPROM),erasable programmable read only memory (EPROM), a memory card or sticksuch as USB memory, a memory chip, a mini disk (MD), a magneto opticaldisc (MO), magnetic tape, a hard disk in a server, a solid state memorydevice or the like, but not limited these.

The hardware platform includes any desired kind of hardware resourcesincluding, for example, a central processing unit (CPU), a random accessmemory (RAM), and a hard disk drive (HDD). The CPU may be implemented byany desired kind of any desired number of processor. The RAM may beimplemented by any desired kind of volatile or non-volatile memory. TheHDD may be implemented by any desired kind of non-volatile memorycapable of storing a large amount of data. The hardware resources mayadditionally include an input device, an output device, or a networkdevice, depending on the type of the apparatus. Alternatively, the HDDmay be provided outside of the apparatus as long as the HDD isaccessible. In this example, the CPU, such as a cache memory of the CPU,and the RAM may function as a physical memory or a primary memory of theapparatus, while the HDD may function as a secondary memory of theapparatus.

In the above-described example embodiment, a computer can be used with acomputer-readable program, described by object-oriented programminglanguages such as C++, Java (registered trademark), JavaScript(registered trademark), Perl, Ruby, or legacy programming languages suchas machine language, assembler language to control functional units usedfor the apparatus or system. For example, a particular computer (e.g.,personal computer, work station) may control an information processingapparatus or an image processing apparatus such as image formingapparatus using a computer-readable program, which can execute theabove-described processes or steps. In the above described embodiments,at least one or more of the units of apparatus can be implemented inhardware or as a combination of hardware/software combination. Inexample embodiment, processing units, computing units, or controllerscan be configured with using various types of processors, circuits, orthe like such as a programmed processor, a circuit, an applicationspecific integrated circuit (ASIC), used singly or in combination.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the appended claims, the disclosure of the presentinvention may be practiced otherwise than as specifically describedherein. For example, elements and/or features of different examples andillustrative embodiments may be combined each other and/or substitutedfor each other within the scope of this disclosure and appended claims.

What is claimed is:
 1. An image inspection apparatus for inspecting animage output on a recording medium by scanning the output image as ascanned image, the image inspection apparatus comprising: an inspectionreference image generator to obtain data of an output-target image usedby the image forming apparatus for an image fomiing operation, and togenerate an inspection reference image using the data of theoutput-target image, the inspection reference image to be used for animage inspection of the scanned image; an image inspection unit todetermine whether the scanned image includes a defect based on acomparison result obtained by comparing a difference between theinspection reference image and the scanned image with a given threshold;a threshold determiner to determine the given threshold based on acomparison result between the inspection reference image having a normalimage condition and the scanned image of threshold setting imageprepared by adding a plurality of artificial defects having differentdefect levels to the inspection reference image; and a defect rangedeterminer to determine a range of defect level of a plurality ofartificial defects having the different levels for the threshold settingimage; wherein the threshold determiner controls generation of theinspection reference image having the normal image condition to be usedfor determining the given threshold, wherein the threshold determinercomputes a difference between the inspection reference image and thescanned image of the threshold setting image for each of the pluralityof artificial defects having the different defect levels, wherein, basedon a difference computed for a defect selected from the plurality ofartificial defects having different defect levels, the thresholddeterminer determines a threshold to be compared with the difference ofthe selected defect to determine whether the scanned image includes adefect; wherein the defect range determiner conducts a defectdetermination process for a range determination scanned image, obtainedby scanning a range determination image displaying a plurality ofdefects having changed levels with a given interval at each of the upperlimit and the lower limit settable for a threshold, wherein the defectrange determiner determines a range of defect level of the plurality ofartificial defects having the different defect levels for the thresholdsetting image based on a defect level of a defect determined as defectin the defect determination process for the range determination image ateach of the upper limit and the lower limit settable for the threshold.2. The image inspection apparatus of claim 1, wherein the rangedetermination scanned image is divided into a plurality of area asdivided areas, and the defect range determiner determines a defect foreach of the divided areas of the range determination scanned image,wherein the defect range determiner refers to information of positiondisplaying each of the plurality of defects in the range determinationimage, and determines a range of defect level of the plurality ofartificial defects having different defect levels for the thresholdsetting image based on a level of defect corresponding to a position ofthe divided area determined as defect in the range determination scannedimage.
 3. The image inspection apparatus of claim 1, wherein thethreshold setting image is prepared by adding a plurality of artificialdefects having different levels for different types of defect to thereference inspection image, wherein the range determination imageincludes images displaying a plurality of defects by changing levels forthe different types of defect with a given interval, wherein the defectrange determiner determines a defect range for a plurality of artificialdefects having different levels for each of the different types ofdefect prepared as the threshold setting image based on a level ofdefect determined as defect for each of the different types of defect ina defect determination process at each of the upper limit and the lowerlimit settable for the threshold.
 4. The image inspection apparatus ofclaim 1, wherein the threshold determiner outputs display informationfor displaying a selection screen for selecting a defect from theplurality of artificial defects having different defect levels, andrecognizes a defect selected by an operation to the selection screen. 5.The image inspection apparatus of claim 4, wherein the thresholddeterminer outputs display information for displaying a selection screenrandomly arranging the plurality of artificial defects having differentdefect levels in view of the defect levels of the artificial defects. 6.The image inspection apparatus of claim 1, wherein when the inspectionreference image is generated, the inspection reference image generatorfunctions as a part of the threshold detelininer, wherein when thedifference between the reference inspection image and the scanned imageis computed, the image inspection unit functions as a part of thethreshold determiner, wherein when the defect determination process isconducted for the range determination scanned image at each of the upperlimit and the lower limit settable for a threshold, the image inspectionunit functions as a part of the defect range determiner.
 7. An imageinspection system for inspecting an image output on a recording medium,the image inspection system comprising: an image forming unit to conductan image forming operation of a threshold setting image on the recordingmedium, the threshold setting image prepare-able by adding an artificialdefect to an output-target image input to the image forming unit; animage scanner to scan the threshold setting image output on therecording medium to generate a scanned image; an inspection referenceimage generator to obtain data of the output-target image used by theimage forming apparatus for an image forming operation, and to generatean inspection reference image using the data of the output-target image,the inspection reference image to be used for an image inspection of thescanned image; an image inspection unit to determine whether the scannedimage includes a defect based on a comparison result obtained bycomparing a difference between the inspection reference image and thescanned image with a given threshold; a threshold determiner todetermine the given threshold based on a comparison result between theinspection reference image having a normal image condition and thescanned image of threshold setting image prepared by adding a pluralityof artificial defects having different defect levels to the inspectionreference image; and a defect range determiner to determine a range ofdefect level of a plurality of artificial defects having the differentlevels for the threshold setting image, wherein the image formingsection unit conducts an image forming operation of the thresholdsetting image based on the determined range of defect level of theartificial defect, wherein the threshold determiner controls generationof the inspection reference image having the normal image condition tobe used for determining the given threshold, wherein the thresholddeterminer computes a difference between the inspection reference imageand the scanned image of the threshold setting image for each of theplurality of artificial defects having the different defect levels,wherein, based on a difference computed for a defect selected from theplurality of artificial defects having different defect levels, thethreshold determiner determines a threshold to be compared with thedifference of the selected defect to determine whether the scanned imageincludes a defect; wherein the defect range determiner conducts a defectdetermination process for a range determination scanned image, obtainedby scanning a range determination image displaying a plurality ofdefects having changed levels with a given interval at each of the upperlimit and the lower limit settable for a threshold, wherein the defectrange determiner determines a range of defect level of the plurality ofartificial defects having the different defect levels for the thresholdsetting image based on a defect level of a defect determined as defectin the defect determination process for the range determination image ateach of the upper limit and the lower limit settable for the threshold.8. A method of inspecting an image, output on a recording medium, usingan image inspection apparatus, the method comprising the steps of:obtaining an output-target image input to an image fonning apparatus;generating an inspection reference image using data of the output-targetimage; forming a threshold setting image on the recording medium usingthe image forming apparatus, the threshold setting image prepare-able byadding an artificial defect to the inspection reference image; scanningthe threshold setting image formed on the recording medium to obtain ascanned image of the threshold setting image; computing a differencebetween the scanned image and the inspection reference image bycomparing the scanned image and the inspection reference image;determining a threshold , based on a difference computed for a defectselected from the plurality of artificial defects having differentdefect levels, the determined threshold to be compared with thedifference for the selected defect to determine whether the scannedimage includes a defect; conducting a defect determination process for arange determination scanned image obtained by scanning a rangedetermination image, displaying a plurality of defects by changinglevels of different types of defect with a given interval, at each ofthe upper limit and the lower limit settable for a threshold; anddetermining a range of defect level of the plurality of artificialdefects having the different defect levels for the threshold settingimage based on levels of defect determined as defect in the defectdetermination process for the range deteimination image at each of theupper limit and the lower limit settable for the threshold.